Oscillator self-calibration

ABSTRACT

An oscillator assembly includes a scribe seal, an oscillator circuit, and a calibration circuit. The oscillator circuit includes an output. The calibration circuit is coupled to the oscillator circuit. The calibration circuit includes a reference frequency terminal, a conductor coupled to the reference frequency terminal, and an oscillator input terminal. The conductor extends to an edge of the oscillator circuit assembly and penetrates the scribe seal. The oscillator input terminal is coupled to the output of the oscillator circuit.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.16/728,070 filed Dec. 27, 2019, which is incorporated herein byreference.

BACKGROUND

In electronic and computing devices, at least one clock referencegenerally provides a clock signal for synchronizing and scheduling,operations. A variety of approaches exist for generating the clocksignal. For example, oscillators may have quartz crystal resonators,micro-electro-mechanical system (MEMS) resonators, inductor-capacitor(LC) resonators, delay circuitry, and various other components toprovide a clock frequency suitable for a specific application.

SUMMARY

An oscillator circuit assembly and method for in-wafer calibration ofthe assembly are described herein. In one example, an oscillator circuitassembly includes an oscillator circuit and a calibration circuit. Theoscillator circuit includes an input and an output. The calibrationcircuit is coupled to the oscillator circuit, and includes a referencefrequency terminal and a digital phase-locked loop. The digitalphase-locked loop circuit includes an output, a first input, and asecond input. The output of the digital phase-locked loop circuit iscoupled to the input of the oscillator circuit. The first input of thedigital phase-locked loop circuit is coupled to the output of theoscillator circuit. The second input of the digital phase-locked loopcircuit is coupled to the reference frequency terminal.

In another example, an oscillator circuit assembly includes a scribeseal, an oscillator circuit, and a calibration circuit. The oscillatorcircuit includes an output. The calibration circuit is coupled to theoscillator circuit. The calibration circuit includes a referencefrequency terminal, a conductor coupled to the reference frequencyterminal, and an oscillator input terminal. The conductor extends to anedge of the oscillator circuit assembly and penetrates the scribe seal.The oscillator input terminal is coupled to the output of the oscillatorcircuit.

In a further example, a method includes connecting a reference frequencysource to a reference frequency terminal of a wafer comprising a firstoscillator circuit assembly and a second oscillator circuit assembly.The reference frequency terminal is connected to a calibration circuitof the first oscillator circuit assembly via a conductor that penetratesa scribe seal of the first oscillator circuit assembly, and connected toa calibration circuit of the second oscillator circuit assembly via aconductor that penetrates a scribe seal of the second oscillator circuitassembly. The calibration circuit of the first of the first oscillatorcircuit assembly applies a reference frequency received via thereference frequency terminal to calibrate the first oscillator circuitassembly over temperature prior to singulation. The calibration circuitof the second oscillator circuit assembly applies the referencefrequency received via the reference frequency terminal to calibrate thesecond oscillator circuit assembly over temperature prior tosingulation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows block diagram of an example oscillator circuit assemblythat includes built-in self-calibration circuitry in accordance withthis description.

FIG. 2 shows an example wafer that includes multiple oscillator circuitassemblies configured for simultaneous self-calibration in accordancewith this description.

FIG. 3 shows a flow diagram for an example method for simultaneousself-calibration of oscillator circuit assemblies on a wafer inaccordance with this description.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

In this description, the term “couple” or “couples” means either anindirect or direct wired or wireless connection. Thus, if a first devicecouples to a second device, that connection may be through a directconnection or through an indirect connection via other devices andconnections. Also, in this description, the recitation “based on” means“based at least in part on.” Therefore, if X is based on Y, then X maybe a function of Y and any number of other factors.

Oscillator circuit assemblies, including oscillator circuit assembliesthat include micro-electro-mechanical system (MEMS) resonators, aretested and characterized over temperature to enable compensation fortemperature induced frequency drift. Each oscillator circuit assembly isindividually tested and calibrated after the oscillator circuitassemblies have been packaged. Individually testing and calibrating eachoscillator circuit assembly is time consuming and expensive.

The calibration method described herein allows simultaneous testing andcalibration of many oscillator circuit assemblies provided on a siliconwafer. For example, all of the oscillator circuit assemblies provided ona wafer may be simultaneously tested and calibrated for temperatureinduced frequency drift. The oscillator circuit assemblies describedherein include on-die calibration circuitry. To enable calibration, apower source and a reference frequency source are connected to a waferunder test. Power and reference frequency signals are propagated to theoscillator and calibration circuits of each oscillator circuit assemblythrough conductors that penetrate the scribe seals of each of theoscillator circuit assemblies. The wafer is temperature cycled (e.g.,heated to a maximum temperature, and cooled to a minimum temperature)while the calibration circuitry compares the reference frequency signalto an oscillator output signal. As the frequency of the oscillatoroutput signal drifts from the frequency of the reference frequencysignal, the calibration circuit determines and applies a tuning value tocompensate for the drift. That is, over temperature, the calibrationcircuit applies a tuning value to adjust the frequency of the oscillatoroutput signal to match the frequency of the reference frequency signal.The calibration circuit stores the tuning values and a temperature valueat which each tuning value is applied in a non-volatile memory. Inoperation, the stored tuning values may be applied, in conjunction withstored temperature values, to compensate for temperature drift of theoscillator circuit.

FIG. 1 shows block diagram of an example oscillator circuit assembly 100that includes built-in self-calibration circuitry in accordance withthis description. The oscillator circuit assembly 100 includes anoscillator circuit 102 and a calibration circuit 104. The oscillatorcircuit 102 includes a MEMS resonator 114, a crystal resonator, or othertiming circuitry in various implementations. The oscillator circuit 102generates an oscillator output signal 124. The calibration circuit 104is coupled to the oscillator circuit 102.

The calibration circuit 104 includes a digital phase-locked loop circuit106, a control circuit 108, a temperature sensor 110, a memory 112, anoscillator input terminal 104A, and a reference frequency terminal 104B.A conductor 120 extends from the reference frequency terminal 104Bthrough the scribe seal 116 to an edge of the die on which theoscillator circuit assembly 100 is constructed. An input 106A of thedigital phase-locked loop circuit 106 is coupled to the referencefrequency terminal 104B. An input 106B of the digital phase-locked loopcircuit 106 is coupled to an output 102A of the oscillator circuit 102via the oscillator input terminal 104A. An output 106C of the digitalphase-locked loop circuit 106 is coupled to an input 102B of theoscillator circuit 102. The digital phase-locked loop circuit 106compares the reference signal 122 received via the input 106A to theoscillator output signal 124 received via the input 106B, and generatesa tuning value 126 to adjust the frequency of the oscillator outputsignal 124. The digital phase-locked loop circuit 106 provides thetuning value 126 to the oscillator circuit 102, and the oscillatorcircuit 102 applies the tuning value 126 to adjust the frequency of theoscillator output signal 124 to match the frequency of the referencesignal 122 received at the input 106A. For example, the tuning value 126may adjust a value of capacitance in the oscillator circuit 102 toadjust the frequency of the oscillator output signal 124.

The temperature sensor 110 measures the temperature of the oscillatorcircuit assembly 100, and provides temperature measurements 128 to thecontrol circuit 108. The control circuit 108 is coupled to the digitalphase-locked loop circuit 106, the temperature sensor 110, and thememory 112. The control circuit 108 includes an input 108A coupled tothe output 106C of the digital phase-locked loop circuit 106 forreception of the tuning value 126 generated by the digital phase-lockedloop circuit 106. The control circuit 108 includes an input 108C forreception of the temperature measurements 128 provided by thetemperature sensor 110. The control circuit 108 writes the tuning value126 and the temperature measurements 128 into the memory 112. Thecontrol circuit 108 includes an output 108D coupled to an input 112A ofthe memory 112. In some implementations, the control circuit 108 writesthe tuning value 126 into locations of the memory 112 that correspond toa value of the temperature measurements 128. In some implementations,the control circuit 108 is triggered to write the tuning value 126 intothe memory 112 by a change in the temperature measurements 128 or achange in the tuning value 126. Thus, the control circuit 108 may detecta change in the tuning value 126 or a change in the temperaturemeasurements 128, and responsive to the change, write the tuning value126, and the temperature measurements 128 in some implementations, intothe memory 112. The memory 112 may be an electrically erasableprogrammable read only memory, a FLASH memory, a ferroelectric memory,or other non-volatile memory.

The control circuit 108 may also include an output 108B coupled to aninput 106D of the digital phase-locked loop circuit 106. The controlcircuit 108 may provide control information to the digital phase-lockedloop circuit 106 via the output 108B. In some implementations, a controlsignal may be provided via a conductor that penetrates the scribe seal116, where the control signal indicates to the control circuit 108whether calibration is being performed. Some implementations maydetermine whether calibration is being performed based on the presenceof the reference signal 122. For example, the control circuit 108 may becoupled to the reference frequency terminal 104B for receipt of thereference signal 122 and include circuitry to detect the presence of thereference signal 122. The control circuit 108 may enable the digitalphase-locked loop circuit 106 when the reference signal 122 is present,and disable the digital phase-locked loop circuit 106 when the referencesignal 122 is not present. The control circuit 108 may enable or disablecalibration of the oscillator circuit assembly 100 based on the presenceof the reference signal 122. The control circuit 108 may include ahardware state machine or a microcontroller configured to controlstorage of the tuning values 126 in the memory 112, and provide otherfunctionality of calibration of the oscillator circuit assembly 100 asdescribed herein.

When the oscillator circuit assembly 100 is operating normally (i.e.,not calibrating), then the control circuit 108 may read the tuningvalues 126 from the memory 112 based on the temperature measurements 128provided by the temperature sensor 110, and provide the tuning values126 read from the memory 112 to the oscillator circuit 102 to adjust thefrequency of the oscillator output signal 124.

FIG. 2 shows an example wafer 200 that includes multiple oscillatorcircuit assemblies 202 configured for simultaneous self-calibration inaccordance with this description. Each oscillator circuit assembly 202is an implementation of the oscillator circuit assembly 100. The wafer200 may include any number of the oscillator circuit assemblies 202. Thewafer 200 includes power terminals 204 and 206, and a reference signalterminal 208. Any number of the oscillator circuit assemblies 202 may becoupled to the power terminal 204, the power terminal 206, and thereference signal terminal 208. For example, all of the oscillatorcircuit assemblies 202 provided on the wafer 200 may be coupled to thepower terminal 204, the power terminal 206, and the reference signalterminal 208. When the oscillator circuit assemblies 202 are to becalibrated, the power terminal 204 and the power terminal 206 areconnected to a power source, and the reference signal terminal 208 isconnected to a reference signal source, such as a rubidium oscillator orother accurate low-drift clock source.

The oscillator circuit assemblies 202 detect the reference signal andenter calibration mode. The wafer 200 is disposed in temperature chamberand temperature cycled across the predetermined range of calibrationtemperatures. As the temperature of the wafer 200 changes, in each ofthe oscillator circuit assemblies 202 the digital phase-locked loopcircuit 106 generates tuning values 126 to adjust the oscillator outputsignal 124, and the control circuit 108 stores the tuning values 126 inthe memory 112. Because the digital phase-locked loop circuit 106 isvery fast, the 102 remains locked to the reference signal source as thetemperature of the wafer 200 changes. This advantageously allows fortemperature change and calibration at a relatively fast rate. Incontrast, for each temperature at which calibration is performed, othercalibration techniques require that before calibration is performed thetemperature of an integrated circuit be allowed stabilize, which maytake several minutes. Thus, each of the oscillator circuit assemblies202 simultaneously self-calibrates, without allowing soak time fortemperature stabilization, which reduces the time and cost associatedwith calibrating the oscillator circuit assemblies 202 relative topost-singulation calibration.

FIG. 3 shows a flow diagram for a method 300 for simultaneousself-calibration of oscillator circuit assemblies on a wafer inaccordance with this description. Though depicted sequentially as amatter of convenience, at least some of the actions shown can beperformed in a different order and/or performed in parallel.Additionally, some implementations may perform only some of the actionsshown. At least some operations of the method 300 may be performed by animplementation of the oscillator circuit assembly 100.

In block 302, multiple oscillator circuit assemblies 202 formed on thewafer 200 are to be simultaneous calibrated. For each oscillator circuitassembly 202, the circuitry of the oscillator circuit 102 and thecalibration circuit 104 have been formed on the 200, and the 114 hasbeen coupled to the oscillator circuit 102. A power source is connectedto the power terminal 204 and the power terminal 206, and a referencefrequency source is connected to the reference signal terminal 208. Forexample, a reference voltage, such as ground is connected to the powerterminal 204, an operating voltage, such as 1.8 volts, is connected tothe power terminal 206, and a rubidium oscillator is connected to thereference signal terminal 208.

In block 304, the power source and the reference frequency source areconnected to each of the oscillator circuit assemblies 202 to becalibrated. That is, conductors carrying the power signals and thereference frequency signal received at the power terminal 204, the powerterminal 206, and the reference signal terminal 208 pass through thescribe seal of each of the oscillator circuit assemblies 202 to connectthe power signals and the reference frequency source to each of theoscillator circuit assemblies 202.

In block 306, each of the oscillator circuit assemblies 202 detects thereference signal 122, enables calibration, and begins to apply thereference frequency to calibrate for frequency drift.

In block 308, the wafer 200 is disposed in a temperature chamber, andthe temperature of the wafer 200 is increased to a predetermined upperlimit, and/or the temperature of the wafer 200 is decreased to apredetermined lower limit to allow the oscillator circuit assemblies 202to test and adjust the oscillator frequency over the range of appliedtemperatures.

In block 310, the digital phase-locked loop circuit 106 of eachoscillator circuit assembly 202 compares the reference frequency to thefrequency of the oscillator signal generated by the oscillator circuit102 of the oscillator circuit assembly 202.

In block 312, the digital phase-locked loop circuit 106 of eachoscillator circuit assembly 202 generates a tuning value 126 to adjustthe frequency of the oscillator output signal 124, so that the frequencyof the oscillator output signal 124 matches the reference frequency.

In block 314, each of the oscillator circuit assemblies 202 senses achange in the temperature of the wafer 200. That is, the temperaturesensor 110 of each oscillator circuit assembly 202 senses a change inthe temperature of the oscillator circuit assemblies 202, and thetemperature sensor 110 provides a temperature measurement 128 to thecontrol circuit 108 indicating that the temperature of the oscillatorcircuit assembly 202 has changed.

In block 316, each of the oscillator circuit assemblies 202 stores thetuning values 126 applied to adjust the frequency of the oscillatoroutput signal 124 in the memory 112 with associated temperatureinformation (e.g., the temperature measurements 128). For example, thecontrol circuit 108 may store the tuning value 126 responsive todetection of a change in the temperature measurements 128 or responsiveto detection of a change in the tuning value 126.

Modifications are possible in the described embodiments, and otherembodiments are possible, within the scope of the claims.

What is claimed is:
 1. An oscillator circuit assembly comprising: anoscillator circuit having an input and an output; and a calibrationcircuit coupled to the oscillator circuit, and comprising: a referencefrequency terminal; and a digital phase-locked loop circuit comprising:an output coupled to the input of the oscillator circuit; a first inputcoupled to the output of the oscillator circuit; and a second inputcoupled to the reference frequency terminal.
 2. The oscillator circuitassembly of claim 1 further comprising: a scribe seal; and a conductorcoupled to the reference frequency terminal, the conductor extending toan edge of the oscillator circuit assembly and penetrating the scribeseal.
 3. The oscillator circuit assembly of claim 1, wherein: thedigital phase-locked loop circuit comprises a third input; and thecalibration circuit comprises a control circuit comprising: an inputcoupled to the output of the digital phase-locked loop circuit; and anoutput coupled to the third input of the digital phase-locked loopcircuit.
 4. The oscillator circuit assembly of claim 3, wherein: theinput of the control circuit is a first input; the control circuitcomprises a second input; and the calibration circuit comprises atemperature sensor comprising an output coupled to the second input ofthe control circuit.
 5. The oscillator circuit assembly of claim 4,wherein the calibration circuit comprises a memory coupled to thecontrol circuit.
 6. The oscillator circuit assembly of claim 5, whereinthe digital phase-locked loop circuit is configured to generate a tuningvalue based on a difference in a frequency of a reference signalreceived at the reference frequency terminal and a frequency of anoutput signal generated by the oscillator circuit.
 7. The oscillatorcircuit assembly of claim 6, wherein the control circuit is configuredto store the tuning value and a temperature value generated by thetemperature sensor in the memory.
 8. The oscillator circuit assembly ofclaim 1, wherein the oscillator circuit comprises amicro-electro-mechanical system (MEMS) resonator.
 9. An oscillatorcircuit assembly, comprising: a scribe seal; an oscillator circuitcomprising an output; and a calibration circuit coupled to theoscillator circuit, and comprising: a reference frequency terminal; aconductor coupled to the reference frequency terminal, the conductorextending to an edge of the oscillator circuit assembly and penetratingthe scribe seal; and an oscillator input terminal coupled to the outputof the oscillator circuit.
 10. The oscillator circuit assembly of claim9, wherein: the oscillator circuit comprises an input; and thecalibration circuit comprises: a digital phase-locked loop circuitcomprising: an output coupled to the input of the oscillator circuit; afirst input coupled to the output of the oscillator circuit; and asecond input coupled to the reference frequency terminal.
 11. Theoscillator circuit assembly of claim 10, wherein: the digitalphase-locked loop circuit comprises a third input; and the calibrationcircuit comprises a control circuit comprises: an input coupled to theoutput of the digital phase-locked loop circuit; and an output coupledto the third input of the digital phase-locked loop circuit.
 12. Theoscillator circuit assembly of claim 11, wherein: the input of thecontrol circuit is a first input; the control circuit comprises a secondinput; and the calibration circuit comprises a temperature sensorcomprising an output coupled to the second input of the control circuit.13. The oscillator circuit assembly of claim 11, wherein: the output ofthe control circuit is a first output; the control circuit comprises asecond output; and the calibration circuit comprises a memory comprisingan input coupled to the second output of the control circuit.